Quick calculation and 2 questions

Apr 2, 2019

i am thinking about going mobile, creating my own camper and have some questions regarding electric and power..

i have an item, that runs at 230v and 130watts every hour of the day that i would need to take with me.

now, using a 12v system. or even a 24v system

how many amp hours would i need?
how much in watts, solar would i need to ensure it fully charged the batteries?

any help would be appreciated.. PS. i dont want to know the best, just how much would be required for that item alone.
Oct 8, 2006
130W is 130W no matter what the supply voltage. However converting from 240V to 12V or 24V has inefficiences so it does not follow that the power/current drawn will be mathematically related.
In simple terms - 130W at 240V is about 550mA. 130W at a nominal 12V is almost 11A, so to keep that running for 24 hours means you would need a nominal (say) 270Ah. That is a very big and expensive battery. At 24V you would need about half that capacity.
I keep saying nominal as the battery plate voltage will fall as its state of charge falls. If the load is resistive - such as a fridge - then the current drawn will also fall and the cooling effect in the fridge will suffer. Ergo to keep it healthy you are going to need probably 50% more battery capacity to ensure the voltage doesn't drop too much. If it is a fridge there is no thermostatic control on 12V. Running from 12V is designed to keep an already cold fridge cold whilst you travel.
Don't forget that you have got to charge the battery again as well.
If it is a fridge, and you have no mains, maybe try running it on gas?
If you want to run it from a solar panel, then the panel would need to be rated at least the same as the power drawn and probably quite a bit of overhead. You would also need the sun to shine 24/7! :S
Mar 14, 2005
Hello Krapplebyt

Woodentop has outlined the basics very well. It looks like you'd need a big battery, a substantial solar array to ensure it gets a decent charge.

I appreciate that you may prefer not to disclose what your trying to power, but we might be able to offer more focused advice if we knew what you are trying to power.


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